UPSC Prelims 2025 Q81: Science & Technology – Rare Earth Elements
Consider the following statements:
Statement I:
Some rare earth elements are used in the manufacture of flat television screens and computer
monitors.
Statement II:
Some rare earth elements have phosphorescent properties.
Which one of the following is correct in respect of the above statements?
- (a) Both Statement I and Statement II are correct and Statement II explains Statement I
- (b) Both Statement I and Statement II are correct but Statement II does not explain Statement I
- (c) Statement I is correct but Statement II is not correct
- (d) Statement I is not correct but Statement II is correct
Answer: (a) Both Statement I and Statement II are correct and Statement II explains Statement I
Explanation
Rare earth elements in screens
| Statement | Verdict | Fact |
|---|---|---|
| I. Some rare earth elements are used in the manufacture of flat television screens and computer monitors | Correct | Europium, terbium and yttrium are used as phosphors |
| II. Some rare earth elements have phosphorescent properties | Correct | They glow when struck by electrons or ultraviolet light |
Does II explain I? Yes. These elements are used in screens because they emit coloured light.
| Element | Colour it gives |
|---|---|
| Europium | Red (and blue) |
| Terbium | Green |
| Yttrium | Host material for the red phosphor |
About rare earths:
| Feature | Detail |
|---|---|
| Number | 17 elements: 15 lanthanides, scandium and yttrium |
| Other uses | Strong magnets (neodymium), batteries, lasers |
| In India | Found in monazite beach sands of Kerala, Tamil Nadu and Odisha |
Answer: (a) Both Statement I and Statement II are correct and Statement II explains Statement I.
Why each option is right or wrong
- (a) CORRECT. Both are true, and the phosphorescent property is why rare earths are used in screens.
- (b) Incorrect. Statement II does explain Statement I.
- (c) Incorrect. Statement II is correct: some rare earths are phosphorescent.
- (d) Incorrect. Statement I is correct: rare earths are used in screens and monitors.
Key point
Rare earths (17 elements): europium, terbium and yttrium are phosphors that give colour to screens; neodymium makes strong magnets; India has monazite sands.
Remember
Rare earth phosphors make screens glow.
Common mistakes
- Thinking the two statements are unrelated facts.
- Believing rare earths are truly rare; they are hard to separate, not scarce.
- Forgetting scandium and yttrium among the 17.
Exam tip
Ask 'why are they used in screens?' The answer is Statement II itself.
Sources
- Indian Bureau of Mines — Indian Minerals Yearbook: Rare Earths
- IREL (India) Limited — Rare earths and their applications